1. Field of the Invention:
The present invention relates to a process for separating and recovering brominated acenaphthylene and its condensates in the form of powder from their solution obtained in the production course.
Brominated acenaphthylene and its condensates (designated hereinafter as Con-BACN) are compounds excellent in the uncombustive and radiation-resistive properties and, when they are admixed to various kinds of resins, they can donate to the resins the uncombustive and radiation-resistive properties. Due to the double bonds in their molecules, they can be grafted to a resin by being treated for generation of free radical. They have good immiscibility with resins because of being condensate and therefore they are noted as being capable of maintaining stable noncombustive and radiation-resistive properties for a long period of time (U.S. Pat. No. 4,373,046). Because of these properties, it is expected that Con-BACN will experience increasing use in the preparation of insulating materials for coating cables and for various resins, which materials are employed in the manufacture of parts for atomic reactors, breeder reactors and ionization radiation generators where the radiation resistance and non-combustibility properties of materials are important. The Con-BACN of this invention contains at least one bromine atom on the aromatic ring which is produced by condensation as a result of formal Friedel-Crafts' reaction of brominated acenaphthene to form polymers of the degree of condensation 2 or larger followed by the dehydrobromination reaction, including those brominated acenaphthylene produced by the dehydrobromination of brominated acenaphathene without being condensed. ##STR1## The Con-BACN of this invention is expressed by a general formula [I]; T,0030 where x is an integer 0-1, y is an integer 1-6, and n is an integer 1 or larger. The bond is formed between carbon atoms at the benzyl and the aryl positions of acenaphthylene. Thus, they are for example, ##STR2## Otherwise, ,there may be bonds such as, for example, 1 (or 2), 3'-, 1(or 2), 4'-, 1(or 2), 7'-, and 1(or 2), 8'-. Condensates having the degree of condensation 3 or larger contain any of the bonds mentioned above to increase the number of the constitution units. The condensates referred to in the present invention are those having the degree of condensation 10 or less which are excellent in the immiscibility with resins.
Con-BACN is usually produced in powdery forms, but in resinous conglomerates when recovered by the separation method. Since the compound is intended to be used in a composition with a resin or rubber, the finely divided powdery form is favored for convenience of handling and easy dispersion when admixed to a resin composition.
2. Description of the Prior Arts:
Con-BACN is generally produced by the bromination and condensation of acenaphthene followed by the dehydrobromination reaction. Namely, bromine is added to acenaphthene in a halogenated hydrocarbon solvent in the presence of a Lewis catalyst for the bromination and condensation, and the halogenated acenaphthene condensate obtained is treated with a base such as potassium hydroxide in a methanolic solution for the dehydrobromination reaction. The dehydrobromination reaction is carried out in a solvent which is inactive to a base such as potassium hydroxide in methanol. Thus, the solvents include halogenated and aromatic hydrocarbon solvents. Therefore, the produced Con-BACN is obtained in the form of solution in a good solvent, namely halogenated or aromatic hydrocarbon. For the purpose of recovering Con-BACN in the powdery form by separation from a solution of Con-BACN, methods of reprecipitation are commonly practiced, where the solution of Con-BACN is added to a poor solvent in which Con-BACN has a slight solubility. They include, for example, a method of reprecipitation in acetone (Y. Morita and M. Hagiwara, J. Appl. Polym. Sci., 27, 3329 (1982)), a method of reprecipitation which some of the present inventors previously disclosed in U.S. patent application Ser. No. 615,541 using monohydric aliphatic alcohols containing 3 to 5 carbon atoms for the poor solvent and a method of reprecipitation disclosed in U.S. patent application Ser. No. 615,541 which uses, as poor solvent, saturated aliphatic hydrocarbons containing 5 to 9 carbon atoms.
In these methods Con-BACN can be obtained in the form of powder, but the methods are not free from defect. Particularly, after the reprecipitation procedure, Con-BACN of low degrees of condensation remains dissolved in the filtrate, hence the recovery rate of Con-BACN is lowered. Furthermore, the condensation composition of Con-BACN is somewhat different before and after the reprecipitation and, at the same time, physical properties of the powder are accordingly varied, resulting in leaving problems in the quality control. Additional problems are recovery by separation of the good and poor solvents in the filtrate remaining after the reprecipitation and treatment of the Con-BACN dissolved in the filtrate.
For the purpose of solving these problems, some of the present inventors attempted to develop a process in which saturated aliphatic hydrocarbons were used as poor solvent to reprecipitate Con-BACN, the slurry obtained was distilled to recover the good solvent, powders of Con-BACN were separated and the filtrate was circulatingly used in the subsequent reprecipitation. This was applied for patent (U.S. patent application Ser. No. 615,541).
A good result was obtained by the separation and recovery method of the above-mentioned application, but the method was not free from troubles in operations.
In addition, troubles were also in the working environment and safe handling, because inflammable organic solvents were involved in mixing, stirring, filtering and drying. Thus, this method was not satisfactorily employed as an industrial method for separation and recovery.